* {
    padding: 0;
    margin: 0;
}

div.image-box {
    left: 20px;
    top: 20px;
    width: 300px;
    position: relative;
}

img.main-image {
    width: 300px;
    position: absolute;
}

div.mask {
    position: absolute;
    height: 200px;
    width: 200px;
    background-color: #1939ec;
    opacity: 0.5;
    cursor: move;
    display: none;
}

div.big {
    position: absolute;
    left: 300px;
    top: 0;
    height: 400px;
    width: 400px;
    background-color: pink;
    z-index: 999; /* 提高层级 */
    overflow: hidden;
    display: none;
}